Wireless Networking & Mobile Computing CS 752/852 - Spring 2012

Wireless Networking & Mobile Computing

CS 752/852 - Spring 2012

Tamer NadeemDept. of Computer Science

Lec #5: Advanced MAC SchemesDual Busy Tone & Collision Notification

Page 2 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing

Dual Busy Tone Multiple Access (DBTMA) : A Multiple Access Control

Scheme for Ad Hoc Networks * (Z. Haas and J. Deng)

* Slides adapted from Z. Haas

• This paper completely solves hidden and exposed terminal problems


Key Idea & Goals & Main Results

• Key idea:Continuously protect data packet transmission

Use out-band channels to distribute information

• GoalsSolve hidden & exposed terminal problems

• Main ResultsDBTMA: two out-of-band busy tones & RTS

Completely solve hidden & exposed terminal problems


Related Works

g BTMA (Busy Tone Multiple Access, F. A. Tobagi & L. Kleinrock 1975): Using two channels: data channel & control channel A control center - basestation When base station senses the transmission of a terminal, it broadcasts a busy tone

signal to all terminals, keeping them (except the current transmitter) from accessing the channel

g RI-BTMA (Receiver-Initiated Busy Tone Multiple Access, C. Wu & V. O. K. Li 1987) Time is slotted (similar to slotted ALOHA & need time clock synchronization) A packet preamble is sent to intended receiver by the transmitter Receiver sets up an out-of-band busy tone and waits for the data When sensing busy tone, transmitter sends the data packet

g FAMA (Floor Acquisition Multiple Access, C. L. Fuller & J.J Garecia-Luna-Aceves 1995) FAMA-NPC (NPC = on-persistent packet sensing)

o MACA FAMA-NCS (NCS non-persistent carrier sensing)

o Sensing carrier before sending RTS• If clear, sends RTS• Otherwise, waiting a random time, sensing carrier again

o CTS is more larger than RTS


DBTMA • Two narrow-bandwidth tones

• BTt (Transmitter Busy Tone)• Set up by the node which has data to send • Stop when completing transmitting RTS

• BTr (Receiver Busy Tone)• Set up by the node which receives RTS• Stop when completely receives the data packet

• All nodes sensing any busy tone are not allowed to send RTS• Any node sensing no busy tone is allowed to transmit

RTS

CA

DATA

RTSDATARTS

B


Functionalities of Busy Tones

• BTr (set up by receiver)

Notifying the RTS sender that RTS has been received and channel has been acquired

Announcing to its neighbor nodes that it is receiving data packet and they should refrain from accessing the channel

• BTt (set up by sender)

Providing protection for the RTS packet


Seven DBTMA Operation States

• IDLENode with on packets to send stays in IDLE state

• CONTENDNode has data to send but it is not allowed to send RTS, it stays in CONTEND state

• S_RTSNode sending RTS is in S_RTS state

• S_DATANode sending data is in S_DATA state

• WF_BTRRTS packet sender waiting for the ACK from its intended receiver is in WF_BTR

state• WF_DATA

Receiver waiting for DATA is in WF_DATA state• WAIT

Node send out RTS and senses BTr and waits a mandatory time, it is WAIT state


Finite State Machine of DBTMA


More Details for DBTMA

• When A has data to send • Senses BTt and BTr

• If both are clear• Turns on BTt• Sends out RTS and enters S_RTS state• Turns off BTt at the end of RTS transmission and gets out S_RTS state• Sets a timer for expected BTr and enters WF_BTR state

• If BTr is sensed, enters WAIT state and waits for tmw, then enters S_DATA state and sends data packet

• Otherwise, timer goes to zero, A goes to IDLE state

• Enters IDLE state

• Otherwise• Sets a random timer and goes to CONTENT state

• If BTt or BTr is still sensed when timer goes to zero, A goes to IDLE state

• Otherwise, A turns on BTt and enters S_RTS state and sends out RTS if no any busy tone signal is sensed


More Details for DBTMA

• When B receives RTS, B turns on BTr and sets a timer for expected data packet and enters WF_DATA state

• If B has not received data packet before timer goes to zero

B turns off BTr and goes to IDLE state

•Otherwise, B receives data packet and turns off its BTr when completely getting the data packet

When BTr sensed by any Other Node which is in S_RTS state, the node aborts it RTS and goes to IDLE state


Time Diagram of DBTMA

2

receiver ander transmittebetween thdelay n propagatio maximum 2

timewaitingMandatory t mw

RTS

RTS

DATA

DATA

A

B

BTr of B

BTt of A

tmw

RT

S

τC


Channel Throughputs of DBTMA(Single Broadcast Region)

Capacity = 1 Mbps

Data packet = 4096 b

RTS = 200 b

20 nodes in 50 by 50 m^2

Radio transmission range = 35m

Maximum propagation delay = 0.12 μs


Impact of Busy Tone Detection Delay

RTS

RTS

DATA

DATA

A

B

BTr of B

BTt of A

tmw

τC

Busy Tone Detection Delay


Performance Analysis (single broadcast domain case)

• Assumptions:

• A lot of nodes and all nodes are in the same broadcast domain

• No channel fading, capture effect

• Packet collisions are the only reason for packet errors

• Data processing time and transmit/receive turn around time are negligible

• Bandwidth consumption of busy tones is negligible compared with data channel

/1)1()6(P

P t throughpuChannel

t5.0T periodbusy failed Average

6t periodion transmisssuccessfulA

Pion transmissRTS successful ofy Probabilit

ratemean with afficPoisson tr a generately collective nodes All

2 t timewaitingMandatory

tdelay detection Busy tone

τdelayn propagatio way one Maximum

ion time transmissRTS

on timeTransmissiPacket DATA

s

s

df

d

)t(s

wm

d

d

fsd TPt

e


Channel Throughput (ad-hoc network)

Capacity = 1 Mbps

Data packet = 4096 b

RTS = 200 b

Radio transmission range = 2 km

Propagation delay = 6.7 μs


Comparisons of Channel Throughput

Capacity = 256 kbps Data packet = 4096 b RTS = 200 b Each node are 6 km from each other Propagation delay = 20 μs


Comparison of Different Length of Control Packet

Full connected network

Every node randomly choose its destination for each generated data packet

Capacity = 1 Mbps

Data packet size =4096 b

20 nodes in 50 by 50 m^2

Radio transmission range = 35 m

Propagation delay = 0.12 μs


Network Utilization of DBTMA in Multi-Hop Networks

50 nodes in 400 by 400 m^2

Radio transmission range = 100 m

RTS size = 200 b

Packet size = 4096 b

Capacity = 1 Mbps

Propagation delay = 0.33

Packet arrival at each node is Poisson distributed

Each node randomly selects a neighbor as the destination of each packet

Modified DBTMA 4.2

FAMA-NCS 2.4

DBTMA 5.7

RI-BTMA 4.8

MACA 2.2

μs


19

Summary

• DBTMA does solve hidden & exposed terminal problems

• DBTMA is based on the idea presented in RI-BTMA

• Some idea

Using some kind of out-of-band control channel to propagate some info to achieve some performance targets


Towards Collision Detection in Wireless Networks* (Souvik Sen, Naveen Santhapuri,

Romit Roy Choudhury, Srihari Nelakuditi)

* Slides adapted from Souvik Sen

Page 21 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 21

Collision in Wireless Networks

T1 R T2

t0

t1

ACK Timeout

Retransmit

timeCollision


Collision in Wireless Networks

T1 R T2

Collision

t0

t1

Retransmit

time

Not Efficient!

T1 should have stopped right after collision

ACK Timeout


Collision in Wired Networks

✦ Transmitter aborts transmission on collision

✦ Transmitter senses the signal while transmitting✦ If (sensed != transmitted), abort

T1 R T2

Collision

Ethernet BUS

Collision Detection (CSMA/CD)


Is CSMA/CD Beneficial in Wireless?

R2

Collision Detected

Collision

T2T1

R1

T3

R3

Dont Transmit!


Is CSMA/CD Beneficial in Wireless?

R2

Collision Detected

T2T1

R1

T3

R3

Dont Transmit!

Abort Tx!

Collision


Is CSMA/CD in Wireless Beneficial?

R2

Collision Detected

T2T1

R1

T3

R3

Channel free now


Is CSMA/CD in Wireless Beneficial?

R2

Collision Detected

T2T1

R1

T3

R3

CSMA/CD frees the channel for other transmissions

Lets Transmit!


Can we imitate CSMA/CD on Wireless?


Practical Requirements?

1. Transmitter cannot detect collision

• Receiver needs to detect it

TxRx

Collision!





2. Receiver needs to convey

• collision notification to the transmitter

TxRx

Collision!




2. Receiver needs to convey

• collision notification to the transmitter

3. Transmitter needs an additional antenna

• To receive notification

TxRx

Collision!



Overview

MAC

PHYCro

ssLa

yer MAC

PHY Cro

ssLa

yer

Data Transmission (S1)

S=S1

Tx

Rx

If Collision,Notify Tx

If Notification,Abort Tx

Notify Collision (S2)


Overview

S=S1+S2MAC

PHYCro

ssLa

yer MAC

PHY Cro

ssLa

yer


Data Transmission (S1)

S=S1

Tx

Rx




Two Key Challenges

S=S1+S2

2. Detect Collisionin real time

1. Find Notification onListening Antenna

MAC

PHYCro

ssLa

yer MAC

PHY Cro

ssLa

yer


Data Transmission (S1)Tx

Rx




CSMA/CN key idea: Correlation

2. Detect Collisionin real time

1. Find Notification onListening Antenna


Challenge 1: Detecting Notification

• Hard to decode notification on same channel

• Self-signal too strong

• Let Tx and Rx share a unique signature

• Tx correlates with shared signature

• Detects collision notification, aborts

Observe: No decoding, just correlate

MAC

PHY


Notification Signature

Correlation

Self Signal



Whenever there is a notification, there is a jump in correlation

Cor

rela

tion

Sample Number



Data Data

R

Correlate (Sign(R1))

Sign(R1) Sign(R2)

Collision

T1T2

R2R1

Collision Correlation, Notification, and Abort


Data Data

R

Sign(R1)

Corr (Sign(R1))

Notification!Stop Tx

Collision

T1T2

R2R1

Correlate (Sign(R1))

Sign(R1) Sign(R2)

Collision Correlation, Notification, and Abort


Performance Evaluation

• 7 node USRP testbed

• Zigbee CC2420 PHY

• Max data rate: 250Kbps

• Signature size: 5 bytes

• Compare with 802.11-like and PPR

• PPR detects interfered portion of received packet

• Transmitter sends only the interfered portion


Notification Detection at Tx

Notification Signal << Self Signal

How weak can the notification signal be?

MAC

PHY


How weak the notification signal be?

Signalpower

Self Signal

Notification Signal

}18 dB

✔


How weak the notification signal be?

Signalpower

✘}18 dB

Self Signal

Notification Signal


Interference Detection at Rx

• Interference detection accuracy of 93%

• Receiver should detect interference quickly

• Quicker detection Faster Tx abortion

MAC

PHY


Interference Detection: Speed

CSMA/CN predicts collision within 7 bytesBytes after interferer started


Testbed Experimentation

• One link doing CSMA/CN

• CSMA/CN link has an exposed and hidden terminal

• Whenever CSMA/CN link fails due to interference

• CSMA/CN link stops

• Exposed terminal transmits reducing channel wastage


Testbed Throughput

PPR continues to transmit under collision, worse than CSMA/CN


Traced Based Evaluation

Upto 50% gain in per link throughput

50%

Throughput in Kbps


Summary

• CSMA/CN imitates CSMA/CD in wireless

• Rx uses correlation to detect interference

• Tx uses correlation to detect notification

• Others can utilize freed-up channel


Questions

Wireless Networking & Mobile Computing CS 752/852 - Spring 2012

Documents

busy tone signal

rts page

rts packet page

data statewf

band busy tones rts

data packet transmissionuse

data statewaitnode

rts states